A recently discovered metabolite in pregnancy and neonatal urine is 15 alpha hydroxyestriol, commonly known as estetrol, which is unique in that it is fetal in origin. The concentration of estetrol may prove to be a particularly sensitive and reliable indicator of fetal viability as determination of estriol excretion in pregnancy is of limited value in the case of some subjects. Therefore, the primary objective of this proposal is the development of quantitative method for the estimation of estetrol excretion in pregnancy. Estetrol conjugates will be concentrated with Amberlite XAD-2 resin, hydrolyzed, and free estetrol will be derivatized as an acetate which will be purified by TLC prior to quantitation by gas chromatography. It is further proposed to develop a radioimmunoassay of estetrol from plasma. A specific antibody to estetrol will be made by immunization of rabbits with an antigen in which bovine serum albumin will be incorporated in the C-6 position of estetrol. This specific antigen as well as 3H-estetrol with high specific activity will be synthesized. The urinary excretion and plasma concentration of estetrol as well as urinary estriol excretion will be correlated with the clinical status of mothers and their offspring in normal and complicated pregnancies.